Mechanisms of Acid Resistance inEscherichia coli

Abstract

Adaptation to acid stress is an important factor in the transmission of intestinal microbes. The enterobacterium Escherichia coli uses a range of physiological, metabolic, and proton-consuming acid resistance mechanisms in order to survive acid stresses as low as pH 2.0. The physiological adaptations include membrane modifications and outer membrane porins to reduce proton influx and periplasmic and cytoplasmic chaperones to manage the effects of acid damage. The metabolic acid resistance systems couple proton efflux to energy generation via select components of the electron transport chain, including cytochrome bo oxidase, NADH dehydrogenase I, NADH dehydrogenase II, and succinate dehydrogenase. Under anaerobic conditions the formate hydrogen lyase complex catalyzes conversion of cytoplasmic protons to hydrogen gas. Finally, each major proton-consuming acid resistance system has a pyridoxal-5'-phosphate-dependent amino acid decarboxylase that catalyzes proton-dependent decarboxylation of a substrate amino acid to product and CO2, and an inner membrane antiporter that exchanges external substrate for internal product.

Molecular mechanism of pH-dependent substrate transport by an arginine-agmatine antiporter

“…In E. coli, AR2 and AR3 each use two molecular components, a membrane-embedded amino acid antiporter and a cytosolic decarboxylase, to consume and expel intracellular protons (1)(2)(3). AR3 consists of the antiporter AdiC, which exchanges extracellular L-arginine (Arg) with intracellular agmatine (Agm), and the decarboxylase AdiA, which converts Arg to Agm by removing a carbon dioxide molecule from the α-carboxylate group of Arg and thus absorbing an intracellular proton (2)(3)(4)(5)(6). Similarly, AR2 comprises an L-glutamate (Glu):γ-aminobutyric acid (GABA) antiporter GadC and two Glu decarboxylases, GadA and GadB, which convert Glu to GABA (7,8).…”

Identification of Putative Substrates for the Periplasmic Chaperone YfgM in Escherichia coli Using Quantitative Proteomics

“…2A). Some of these could be grouped according to their biological function, for example proteins required for maltose metabolism (MalF, MalP, and MalQ) (21), anaerobic growth with dimethyl sulfoxide (DmsA and DmsB) (22), and survival during gastrointestinal stresses such as low pH and exposure to bile salts (TdcB, TdcC, TdcD, TdcE, Cfa, CadA, GrcA, and HdeB) (23,24). Around a third of the proteins were localized to the cell envelope (as noted by (25,26)) and could be potential substrates of YfgM.…”

Genes commonly involved in acid tolerance are not overexpressed in the plant microsymbiont Mesorhizobium loti MAFF303099 upon acidic shock

“…A mixture of constitutive and inducible strategies can contribute to bacterial survival in an acidic environment, namely, the removal of protons, alkalisation of the external environment, changes in the composition of the cell envelope, production of general stress proteins and chaperones, expression of transcriptional regulators, and responses to changes in cell density (Cotter and Hill 2003;Kanjee and Houry 2013).…”

“…However, the role of important chaperone systems, such as GroEL and DnaK, in acid stress does not seem to be as crucial as described for the heat-shock response in many bacteria. For example, in Escherichia coli, the chaperones so far implicated in acid response are Hsp31, HdeA and HdeB (Kanjee and Houry 2013).…”

“…In E. coli, other genes found to be involved in acid stress response include gad (glutamic acid decarboxylase) and omp (outer membrane protein) genes (Foster 2001), as well as genes encoding components of the electron transport chain (cyo, ndh, sdh and nuo genes) (Kanjee and Houry 2013).…”